1. Technical Field
The present invention relates to an apparatus and method for cleaning a photomask, and more particularly to an apparatus for cleaning a photomask and a method of cleaning a photomask using the same, wherein a metal plate is formed adjacent to an adhesive residue and a laser is irradiated onto the metal plate to thus effectively remove the adhesive residue by heat of the metal plate.
2. Description of the Related Art
With the recent trend for high integration and miniaturization of electric and electronic devices, strict process conditions are required. Particularly, it is important that pollution or injection of impurities in devices or apparatuses for use in processes be prevented and thus devices having fine patterns be manufactured so as to be adequate for optimal designs. The most widely useful to form a fine pattern in a device manufacturing process is a photolithography process by which a fine pattern is formed on a corresponding wafer.
Typically, a photolithography process is performed in such a manner that a photoresist is uniformly applied on a wafer, and the pattern of the photomask is exposed and developed, thereby forming a fine pattern of the photomask on the wafer.
In the photolithography process, the case where the photomask has defects or impurities results in defective wafers, which undesirably causes problems such as low productivity and yield of semiconductor devices.
In particular, a final pattern on the wafer by a photolithography process is not completed by only a single exposure process, but is formed by a plurality of exposure processes depending on the pattern or the degree of integration. Such defects of the photomask are regarded as the more important process factor in proportion to an increase in the degree of integration of the device.
Thus, process conditions have to be improved so as not to pollute the photomask, and also, a pellicle is formed on one surface of the photomask so that the photomask itself is not polluted.
The pellicle is formed by being attached to the top of a pellicle frame which has been attached to the upper surface of the non-pattern region of the photomask, and thus functions to prevent direct adsorption of impurities on the photomask and makes it easy to store and manage the photomask.
As such, the pellicle frame is attached to a quartz plate of the photomask using an adhesive. In the case where the pellicle is polluted, when it is removed, the adhesive for attaching the pellicle frame may be left behind on the quartz plate of the photomask, making it difficult to form the pellicle again. Also, when a photolithography process is carried out in a state of the adhesive being left behind without the pellicle, problems such as low exposure, scattering of light, etc. due to a chemical reaction by the adhesive may occur. Hence, it is important that the adhesive be completely removed.
Conventionally, a chemical wet removal process using sulfuric acid is performed to remove the adhesive from the photomask, but the wet solution or residue may still be left behind on the photomask even after removal of the adhesive, and the pattern of the photomask may be damaged due to sulfuric acid.
To solve problems caused by the wet removal process, Korean Patent Application Publication No. 10-2008-0001469 discloses removal of an adhesive residue by removing a pellicle from a photomask, thermally treating the photomask to thus melt the adhesive, and cleaning the photomask using a dilution solution (SCl) of O3, ammonia (NH4OH) and hydrogen peroxide (H2O2).
However, this method is problematic because heat is directly applied to the photomask, and thus the photomask may become deformed and polluted, and the cleaning solution may be left behind on the surface of the photomask.
To solve problems due to the wet process, thorough research into removal of an adhesive using a dry process as in Koran Patent Application Publication No. 10-2012-0097893 is ongoing recently.
This method is used to directly irradiate a laser onto the pellicle adhesive residue so as to remove the pellicle residue.
Although this method may remove the adhesive residue from the upper surface of chromium (Cr) formed on the photomask, the adhesive organic material existing on the quartz plate is not completely removed.
FIGS. 1A and 1B illustrate the test results using such a prior patent. FIG. 1A illustrates the case where the adhesive residue is left behind on Cr of the photomask, and FIG. 1B illustrates the case where the adhesive residue is left behind just on the quartz plate of the photomask.
As illustrated in these drawings, in the case where the adhesive residue is left behind on Cr, it is removed to a certain extent without damage to Cr after irradiation of a UV laser. However, in the case where the adhesive residue is left behind just on the quartz plate without Cr, even when a UV laser is irradiated, the adhesive residue is never removed. Even at an energy density two times larger than in the test of removing the adhesive residue from the upper surface of Cr, there is no change in adhesive residue. Furthermore, even when several laser irradiations are implemented, no change in adhesive residue occurs.
Therefore, the method of directly irradiating a laser onto the adhesive residue or the quartz plate is disadvantageous because the adhesive residue is not thoroughly removed from the quartz plate.
Also, as a laser is directly irradiated onto the photomask, the range of power of laser usable to prevent damage to the photomask is limited, and thus thorough removal of the adhesive organic material does not occur. Although the laser power has to be increased to completely remove the adhesive organic material, the photomask may be damaged instead.